Apparatus for adjusting resistors



May 23, 1939. H. G RICHTER APPARATUS FOR ADJUSTING RESISTORS Filed Feb. 27, 1935 3 Sheets-Sheet l mmm INVENTOR Henrg Rich'l'er BY ATTORNEYS am May 2a, was

UNITED STATES PATENT OFFICE This invention relates to apparatus for use in the manufacture of resistors, and more particularly for adjusting the resistance value of fllm type resistors. I

5 x A problem of long standing in the manufacture of resistors has been to make the resistors with uniformly correct resistance value. Many manufacturers rely upon subsequent calibration, that is, a large number of resistance elements (hereinafter conveniently referred to as resistors) are made and are subsequently subjected to resistance measurement andclassified in groups according to the resistance reading obtained. One obvious disadvantage of this procedure is that only some of the resistors are of desired measurement, and in the absence of companion orders for resistors of different measurement, the others must be discarded'or made over. One object of my invention is to obviate the foregoing diflilculty.

Some suggestion to the same end has heretofore been made with a view to removing some of the resistance surface, thereby raising the resistance value. This procedure presupposes that the resistors initially have too low a value. If

the resistors are all purposely made too low in value, excessive treatment is required to bring the same up to desired value. Furthermore, the operation of raising the resistance value is a sensitive one, and frequently the treatment goes further than desired, resulting in an element having a measurement too high and not susceptible of additional treatment. In accordance with a further object of my invention, I provide apparatus adapted to either raise or lower the resistance value at will. I further combine with the apparatus an appropriate resistance meter or ohm meter, and each element placed in the apparatus is readily subjected to any necessary raising or lowering of resistance value until it is adjusted to precisely the desired reading. v The resulting elements have an accurately determined measurement instead of merely falling into some classification or range of measurement. Furthermore,

the initial manufacture of the elementsis directed sistance value during the first few hundred oscillations of the contact shoe on the resistance surface, but that thereafter the change in resistance slows down and soon becomes negligible. One

' object of my invention is to remedy this resist- 5 ance variation which takes place during the early life of the unit, and to this end I combine with the aforementioned apparatus appropriate means for burnishing the surface of the unit in simulation of the action of the contact shoe, in conse- 10 quence of which the resistance reading obtained when the unit is adjusted corresponds to the stable value which ordinarily would bereached only after the first period of use and which would differ from the calibration value; This extra 15 burnishing step is optional, for the regular treatment for adjusting the resistance value itself includes considerable rubbing and burnishing.

Another difficulty arises in connection with variable resistance units because these units are 29 frequently stepped or tapered in value. This may necessitate separate treatment or adjust ment of difi'erent parts of the resistor, and another object of my invention is to provide apparatus elements which make possible separate se- 25 lective treatment of any section of the resistor as well as uniform treatment of the entire resistor.

Further objects of my invention are to devise apparatus to which the resistors may be applied 30 in rapid succession and in which they may be treated conveniently and expeditiously by un skilled labor, all with a view to minimizing the cost of the resistors which are sold under highly competitive conditions. 35

To the accomplishment of the foregoing and other objects which will hereinafter appear, my invention resides in the apparatus elements for adjusting resistors, and their relation one to the other, as are hereinafter more particularly de- 40 scribed in the specification and sought to be defined in the claims. The specification is accompanied by drawings, in which:

Fig. 1 is a front elevation of a preferred form of apparatus embodying features of my invention;

Fig. 2 is a section taken in the plane of the line 2-2 of Fig. 1;

Fig. 3 is a horizontal section taken in the plane or" the line 33 of 1;

Fig. 4 is a section taken in elevation in the plane of the line 44 of Fig. 2;

Fig. .5 is a plan view in the plane of the line 5-5 of Fig. Fig. 6 shows in perspective a type of resistor which the present form of my apparatus is best adapted to handle;

Fig. '7 is a schematic wiring diagram for the apparatus;

Fig. 8 is a side elevation of a portion of the apparatus modified for automatic or power oscillation of the resistor support; and

Fig. 9 is a horizontal section in the plane of the line 8-9 of Fig. 8.

Referring to the drawings and more particularly to Fig. 6, I there show a type of resistance element which the specific apparatus here disclosed has been designed to handle. It will be understood, however, that except for structural details, the apparatus is independent of the form of the resistor and may be rearranged to accommodate changes.

The resistance element shown in Fig. 6 is of the type described in my copending application Ser. No. 734,810 filed July 12, 1934, and a process for manufacturing which is disclosed in companion application Ser. No. 734,811 also filed July 12, 1934. The element comprises a ring of insulation i2 the outer periphery of which is coated with a preferably graphitic resistance film I4 the ends of which contact with metallic terminals I6,

which terminals are preferably carried around the edge of the unit to one face, as is indicated at I8. The annulus I2 has a keyway 20 which properly orientates the same with respect to the terminals I8.

Referring now to Figs. 1, 2, and 3 of the drawtags, the resistor I2 is mounted on a preferably rotatable support or table 22 in position to be op erated on by either resistance lowering means 24 or resistance raising means 26, the actual resistance value being continuously indicated on a suitable ohm meter 28, and the means 24 or the means 26 being selectively and if necessary alternately used until the desired resistance value is accurately read on meter 28.

The resistance lowering means rubs and compacts the resistance film, and preferably takes the form of a rotatable wire brush, and I have discovered that, contrary to what might be anticipated, the abrasion of the resistance film by the wire bristles of such a brush does not raise the resistance by removing resistance material from the film, but rather lowers the resistance. This strange result may be due to a compacting of the film which exceeds any eifect caused by possible removal of some of the graphitic matcria'i.

The resistance raising device 26 rubs and partially removes the resistance film, and preferably takes the form of a rotatable cloth polishing wheel. The operation of such a wheel appears to be based on substantial removal of graphitic material, thereby thinning the film and raising its resistance by an amount which far exceeds the efiect of possible burnishing orcompacting of the film by the wheel. 4

Both brush 24 and wheel 26 may be simultaneously driven by a single motor 30. Brush 24 and wheel 26 are preferably mounted at the ends 32 and 34 of a V-shaped frame, the apex 36 of which is oscillatable on an axis coinciding with the shaft 38 of driving motor 30. A handle 40 at the end 32 of the frame makes it readily possible to oscillate the frame from one side to the other, thereby bringing either the brush 24 or wheel 26 into rubbing engagement with the periphery of resistor l2.

The motor shaft 38 carries a pair of superposed sprocket gears 42 and 44 which respectively drive 68 and wheel 26 may be replaced by loosening nut 60. Brush 24 is preferably protectively housed by a shield 62 detachably secured to the bearing 64 by means of a set screw 66.

The V-frame comprises a main plate 68 which has depending bearings 64 and10 formed integrally therewith, as well as the center bar of handle 40, and rearwardly projecting motionlimiting stop arms I2 and 14 best shown in Fig. 3. The stop arms are each fitted with adjustable stop screws 16 located for cooperation with a fixed stop pin 18. The motion-limiting mechanism is not essential, but is desirable to prevent a careless operator from applying excessive pressure on a resistor being treated.

The chain drive mechanism is enclosed and the V-frame completed by an upwardly dished sheet metal housing 80 having an outwardly turned bottom flange 82 secured to the main frame plate 68 by screws 84. It will be understood that because the axis of driving sprockets 42 and 44 coincides with the axis of oscillation of the frame, there is no change whatsoever in the relatively free frictionless drive of the brush and wheel regardless of the position of the frame. It will also be understood that a gear train or a belt drive may be used in lieu of the chain and sprocket ,drive shown, and that the axis of motor 30 may be displacedfrom its present location and geared or otherwise connected to the sprocket wheels 42 and 44, but the latter are preferably kept at the pivot of the frame as here illustrated.

The resistor I2 is mounted on a rotatable support 22 which is preferably driven by an independent motor 90 and in the present case motor 90 is mounted subjacent support 22 by means of bracket 52 and is connected directly thereto by a vertical shaft 94.

Referring now to Fig. 4, the support 22 comprises a sleeve of insulation surrounding a metallic tube 98. Motor shaft 84 is received within tube 88 and is keyed to the assembly'by a transverse pin I00. The upper end of sleeve 96 has fitted therein three metallic pins I02, I04 and I06 best shown in Figs. 4 and 5. Pins I02 and 1184 are electrically connected to slip rings I08 and H fitted near the lower end of sleeve 96. Pin I06 is devoid of electrical connection and is employed primarily to provide a level three-point support for the resistor I2. A metallic collar H2 is fitted over the upper end of sleeve 96 in order to prevent wear when bringing the brush 24 or wheel 26 against the resistor. It will be understood of course that the overall diameter of sleeve M2 is less than the diameter of the resistor I2. It will also be realized from inspection of Figs. and 6 that contacts I02 and I04 are properly located for engagement with the metallic terminals l8 of the resistor The slip rings I08 and H0 are contacted by suitable brushes I I4 and I I6 resiliently urged into engagement with the slip rings and electrically connected through'conductors [I8 and I20 to the ohmmeter 28 and associated energy source and circuits. The brushes are mounted in an insulation block I22, itself supported on a bearing plate J24 of the machine frame I26. The sleeve 96 may be provided with a collar I28 which prevents thedeposit on the sliprirmsotdirtandabratbd material vresulting from the operation of the machine.

Theresistor llisreadilyappliedtoorremoved from the support 22 by a clamp bly comprising a pin ill dimensioned to be received within tube 98 andcarryingahandie I32 atitsupper end and atransversepin lunearitslowerend. Between the handle and pin are located a compression spring I38 and an dished clamp plate or-cup III. The top of tube ll is cut to form diametrically opposed bayonet slots ill best shown in Fig. 5. The side of tube .0 just above support 22 is fitted with a key ll! dimensioned to mate with the keyway 2. on the resistor II. It will be'understood that to mount resistor l2 in place it is merely ,n to slip the same over the upper end of tube 98 and to then apply the clamp assembly by means of handle I32 until pin I34 is anchored in bayonet slots I, at which time spring I36 bears downwardly -on cup I38 which in turn seats the resistor 12 accurately on the pins III, I and I, the resister being held in proper register and being compelled to-rotate by reason of key 2.

I have heretofore mentioned that the operation of adjusting the resistance may be combined with a burnishing of the film intended to stabilize the resistancevto a value which normally would be attained only after initial period of use. For this P I provide aburnishing shoe l bestshownin Figs.2and 3, andoseillatably mounted on a block I secured at the upper end of a leaf spring I, the lower end 0! which is attached to the insulation bnmh block I22, preterably by means including the lower end of an upstanding post I50 carrying an adjusting screw I52. This arrangement is clearly shown in Fig. 8 in which, however, the burnishing shoe I has been removed from block I. It is manifeat that during the adjusting operation and whiletheresistorisbeingrotatedbymotor 9|,thesurfaceisbeingburnhbedbyshoe I, thus simulating the action of the contact shoe subsequentlyused in the complete resistance unit andtherebybrlngingtheflhntostabiliaedresistance value.

The apparatus as so far described is particularly satisfactory formewith uniform resistance elements. In some cases, however, the rdstor isstepped or tapered invaiue. ,the useful or resistance coated periphery oi the element may be divided into, say four parts, each of which may have adiflerent deslredruktivity. Insuchcaseitisdesiralietoprovideforsepa- .ratetoftheresistanceofthedifluentseetionstoritmaybenecesmrytochame theresistanceofmesectimlmtnotofanother section.

Fbrthispurposetheruktorrotatimnmtor. isdeandthe reshtormpport 22 is treated'asan osdllatahleratherthanarotatablesupport. Shaftllhasmountedthereona wheel lflwhichmaybemovedmanuallytopositimoroscilhtempportfiasdesired. Ashere ilhlstratedthewheel lilmybeacamnwheel having radial holes II to receive 1 theinnerendofanapm'qniatehamleoreapstanbarl. Theholaliiueprdu'ablydisposedinsuitablehcatimrdatlvetothekeyand contacts on therwktor support so that each -capstanholewillconespondtoonesectionofthe steppedvresistor. In opentionit will beunderstoodthat withnwtorli I Ilrunning,thempstanbar lilis "thesupportandtheoveraliadjusted tothedesiredvaiue. Thecalstan iorthesupportisdesirahlebecauseonceina whileduemsomeerrororbecauseoffirstattempts iomeetsome new t. one section of complete batches of the units may run toohighortoolowinresistanoevalueanditis onlythatsectionwhichneedstobetreated. The necessary change in rmistance of the maybegaugedbyasimilarchangeinthemeter readingiortheoverallmsistanee.

In actual practice the procedure followed with steppedunitsistoselectafewsampleunitsirom eachbateh. Theselmitsaretieaieduniformiy tobringtheoveralltodesiredvaiue. Theyarethencalibmtedinaspedalfixtumin ordertoobtainareadingfortheindividualm- AsbeforestatedJnmmteases thesectionshaveihedesiredvahiewithinper- V missible engineering tolerance. Insueh case, the

batchistreatedjustlikeauniformmsistor. Occasionallmonesectionmayhavearesistance vaiiuetoohighortoolow. InthatcaseJhebateh whenflrstappliedtotheappu'atusis mttotheineox-rectsecflomand hum-r isalsotmatedasauniformimitto obtainfliedesiredoverallrmding.

ottheioregdnglpretertoconuol thenmtmsflandllbytheswitehingmementilhmtratedinligflhinwhichitwillbesem thatthebrmhmotorflandtheresistormotor slarebothsimm'de-ener. gimdbyamaincontmlswitehlilmovidedtlnt supplementalswiteh lilisclosembutonthe otherhand,whenswitdilflis l fl ,motorlis deadandswiteh I oontmlsonlynntor'. 'nmeswitebesmaybelomtedasshownmml.

-Infaet,theopcatorneedoonhnlonlyaslngle switeh,namelyswitch IIIJofIhmabatdnof uniform redstors are being treated, the switch lilismedtostartandstoptheamrahlsinelmiingbothmotmawhereaswhmabatehotstqiped mmmmfllmofm fmisn mimnlyanavmuno erainrmanipulatesswitmlilasastartingand switchjustasbefm'e 'lheoscllhtionoftheldstorsumortnfm stqmedmiltsmaybepertormedlutmnathlly imderpowerhnteadofmamnlly andaslight. modification forthispurpcseisfllmtratedhi Figsflandfl. Intheseflguresitwillbeobservedthattheshattofmotm'anettmded belowthemholllngandclnlcawqm "lmgnhhuwithawmmaearlilmounted attheinnermdofashattlflcaniedina ness of the, brush.

end of a rocking bar or plate I80, the. center hearing or hub I82 of which oscillates freely on motor shaft 94 and the opposite end I84 of which is turned upwardly and apertured at I86 in alignment with the capstan holes I56. A small capstan pin I88 is readily slipped through hole I86 into one of the capstan holes I58. When motor 30 is energized, the resistor is oscillated under power. When another section of the resistor is to be treated, it is merely necessary to retract capstan pin I88 and to thereupon reinsert the same in a different capstan hole.

It will be understoodthat when treating uniform resistors it is simply necessary to omit the use of the capstan pin I88, in which case the capstan wheel I54 rotates freely under the drive of motor 80 just as was described in connection with Figure 1.

The tips of the bristles of wire brush 24 bend somewhat and have a burnishing action. They have a tendency after long use to become excessively bent and this decreases the effective- Instead of discarding the brush, it may be given, renewed life by simply reversing the direction of rotation of the same. For this purpose, motor 38 is preferably made reversible, and I provide a switch I90 (see Fig. 1) for occasionally reversing the direction of rotation of the motor. Switch ISO is a-double pole double throw switch connected in the conductors leading to the field of motor 30. The linear speed of the brush differs from that of the reance value of resistors will be apparent from J the foregoing detailed description thereof. The

apparatus is relatively compact and inexpensive and is exceedingly convenient inuse. The resistors may be brought to exact desired resistance value with extreme rapidity and ease by unskilled labor, because the large resistance meter dial directly in front ofthe operator accurately shows the resistance value and the V-frame is readily shifted to one side or the other as the indicator needle moves to one side or the other past the desired value (which of course is temporarily shown by a conspicuous mark) for any given batch of. units being worked on. To the operator the sensation is exactly as though the movement of the handle is itself causing the indicator needle to move. The resistor is readily applied to and removed from the apparatus. During its treatment it is burnished to stabilize its resistance value. Non-uniform or stepped resistors may be treated as well as uniform resistors.

It will be apparent that while I have" shown and described my invention in preferred form, many changes and modifications may bl made in the structures disclosed without departing from the spirit of the invention defined in the following claims. I

I claim: Y

1. Apparatus for adjusting the resistance value of a circular resistor, said apparatus comprising a support rotatable on a vertical axis for redriven during oscillation of the frame, said frame being so disposed with relation to said resistor support that oscillation of the frame in one direction brings the rotating brush into contact with the rotating resistor, while oscillation of the frame in opposite direction brings the rotating wheel in contact with the rotating resistor.

2. Apparatus for adjusting the resistance value of a circular resistor, said apparatus comprising a support rotatable on a vertical axis for receiving and holding the resistor, a frame oscillatable about a vertical axis displaced from the support,- a wire brush rotatably mounted on one part of said frame, a cloth polishing or bufiing wheel rotatably mounted on another part of said frame, a driving motor, driving connections between said motor and said brush and wheel, whereby the brush and wheel are simultaneously driven during oscillation of the frame, said frame being so disposed with relation to said resistor support that oscillation of the frame in one direction brings the rotating brush into rubbing contact with the resistor, while oscillation of the frame in opposite direction brings the rotating wheel into rubbing contact with the resistor, and a wheel on said support to facilitate oscillation of the support in order to rub a part only of the periphery of the resistor on the support.

3. Apparatus for adjusting the resistance value of a circular resistor, said apparatus comprising a support rotatable on a vertical axis for receiving and holding the resistor, an optionally usable motor beneath said support for rotating the same,

a frame oscillatable about a vertical axis displaced from the support, a wheel rotatably mounted on one part of said frame for rubbing, compacting and lowering the resistance, a wheel rotatably mounted on another part of said frame for rubbing, partially removing and raising the resistance, a second driving motor, driving connections between said second motor and said wheels,whereby the wheels are simultaneously driven during oscillation of the frame, said frame being so disposed with relation to said resistor support that oscillation of the frame in one direction brings one of the rotating wheels into rubbing contact with the resistor, while oscillation of the frame in opposite direction brings the other rotating wheel into rubbiu contact with the resistor, contacts on said support engaging the terminals of the'resister, a meter suitably connected through said contacts to indicate the resistance of the resistor, and a wheel on said resistor support to facilitate oscillation of the support in order to rub a part only of the periphery of the resistor on the support.

4. Apparatus for adjusting the resistance value of a circular resistor, said apparatus comprising a support rotatable on a vertical axis for receiving and holding the resistor, a motor beneath said support for rotating the same, a frame oscillatable about a vertical axis displaced from the support, a wire brush rotatably mounted on one part of said frame, a polishing or bufling wheel otatably mounted on another part of said frame,

' a driving motor, driving connections between said said brush and wheel, whereby the wheel are simultaneously driven during oscillation of the frame, said frame being so disposedwithrelationtosaidresistor thatoscillation of theframe in one direction brings the rotating brush .into contact with the resistor, while oscillation of the frame in opposite direction brings the rotating wheel in contact with the mister, contacts on said support engaging the terminals of the resistor, a meter suitably connected through said contacts to indicate the resistance of the resistor, a switch controlling the energization of both motors, a second switch for de-energizing the resistor rotating motor, and means to facilitate oscillation of the support when the second switch is open.

5. Apparatus for adjusting the resistance value of a circular resistor, said apparatus comprisinl; a rotatable support for receiving. and holding the resistor, a frame oscillatable about an axis displaced from the support, a wire brush rotat-, I

ably mounted on one arm ofsaid frame, a cloth polishing or builing wheel rotatably mounted on the other arm of said frame, a driving motor, driving connections between said motor and said brush and wheel, whereby the brush and wheel are simultaneously driven during oscillation of the frame, said frame being so disposed with relation to said resistor support that oscillation of the frame in one direction brings the rotating 'brmh into rubbing contact with the resistor,

' while oscillation of the frame in opposite direcmounted on another part of said frame, a driving motor, driving connections between said motor and said brush and wheel, whereby the brush and wheel are simultaneously driven during oscillation of the-frame, said frame bang so disposed with relation to said resistor support that oscillation of the frame in one direction brings .the

' rotating brush into contact with the resistor,

while of the frame in opposite direction tuscomprisingrneanstosupportthereshtona rotatable wire brmh for rubbing and thereby compacting the resistance fllm, amotor for rotating said brush. means to cause relative movement of the brush and the resistor support whereby direction transverse offthe axis of rotation of the support, a wire brush rotatably mounted on said frame at one side of the support, a polishing or bufiing wheel rotatably mounted on said frame at the opposite side of the support, motor means. for driving said support, said brush, and said wheel, the driving connections to said brush and wheel being such that the brush and wheel are simultaneously driven during movement of the frame, said frame being so disposed with relation to said resistor support that movement of the frame in one direction brings the rotating brush into contact with the, rotating resistor, while' movement of the frame inrthe opposite brings the rotating wheel in contact with rotatingresistor.

9. Apparatus for adjusting the resistance value of a resistor, said apparatus comprising -arotstabiesupportforreceivingandbolding bringstherotatingwheeiincontactwiththere-' sistonacapstanwheelonsaidresistorrotating shaft,acapstan bar-for oscillatingthesupport,

and power meam geared to said motor for oscilthe resistor, an optionally useable motor for rotating said support, a frame mounted for movementinadirectiontransverseoftheaxisofthe support, a wheel rotatably mounted on one part of said frame for rubbing, compacting and lowering the resistance, a wheel rotatably mounted on another part of said frame for rubbing, partially removing and raising the resistance. a second driving motor, driving connections between said contactstoindicatethereshtanceoftheresistor.

HENRY G. RICHTER. 

